Fe₂N nanoparticles boosting FeN_x moieties for highly efficient oxygen reduction reaction in Fe-N-C porous catalysts

Replacing Pt-based electrocatalysts for the oxygen reduction reaction (ORR) with high performance and low-cost non-precious metal catalysts is crucial for the commercialization of fuel cells. Herein, we present a highly efficient Fe-N-C porous ORR electrocatalyst with FeN_x moieties promoted by Fe₂N nanoparticles derived from Fe-doped zeolitic imidazolate framework. The best-performing Fe-N-C/HPC-NH₃ catalyst exhibits a superior ORR activity with an onset (E₀) and half-wave (E_1/2) potential of 0.945 and 0.803 V (RHE), respectively, which is comparable to those of the commercial Pt/C in acidic media. Probing and acid-leaching experiments prove that FeN_x moieties play an important role in the ORR and the Fe₂N can further improve the ORR activity. Density functional theory calculation reveals a synergistic effect that the existence of Fe₂N weakens the adsorption of ORR intermediates on active sites and lowers the reaction free energy of the potential limiting step, thus facilitating the ORR. Both experimental evidence and theoretical analysis for the enhancement of ORR activity by Fe₂N decoration in Fe-N-C catalyst might inspire a new strategy for rational design of high performance non-precious metal catalysts.